Electrical transmission of pictures



Dec. 4, 1928.

E. F. W. ALEXANDERSON ELECTRICAL TRANSMISSION OF PICTURES Filed Oct. 19,1926 3 Sheets-Sheet l Inventor-z Er-nstEWALexanders on,

His Attor'rleg.

Dec. 4, 1928. 1,694,301

E. F. w. ALEXANDERSON ELECTRICAL TRANSMISSION OF PICTURES Filed Oct. 19,1926 3 Sheets-Sheet 2 E rnst E W Alexander-son, by His Attorneg.

E. F. w. ALEXANDERSON ELECTRICAL TRANSMISSION OF PICTURES Dec. 4, 1928.

Filed Oct. 19, 1926 3 Sheets-Sheet Inventor:

ErntFM/Alexgnderson,

b His Attorneg.

Patented Dec. 4, 1928.

UNITED STATES PATENT Fries.

ERNST F. W. ALEXANDERSON, OF SCHENECTADY,- NEWYORK, ASSIGNOR TO GENERALELECTRIC COMPANY, A. CORPORATION OF NEW YORK.

ELECTRICAL TRANSMISSION OF PICTURES.

Application filed October 19', 1926. Serial. No 142,734.

invention relates to the electrical transmission of pictures and anobject of my invention is the provision of improved methods and meansfor the rapid and eflicient I transmission of pictures by electricalmeans.

My invention will be better understood from the following descriptiontaken in connection with the accompanying drawing, and its scope will bepointed out in the appended claims.

Referring to the drawings, Figs. 1 and 2 are a diagrammaticrepresentation respectively of a transmitting apparatus and a receivingapparatus embodying my invention; Fig. 3 is a diagram similar to Fig. 2but drawn to a larger scale; and Figs. 4, 5 and 6 are modificationsthereof. a

The picture to be transmitted may be an ordinary still picture, a movingpicture,- or a view, and by the term picture as used throughout thisdescription and in the claims I in tend to include all forms ofpictures, draw-,

ings, printed pages and views of either still or moving objects. In Fig.1 I have chosen to illustrate my invention being used to transmit ascene or view 1 of two moving characters. In front of the scene is theapparatus for scanning the picture and producing electrical variationscorresponding with'the variations of the picture as determined by theunit areas thereof. As shown, it comprises'a hollow cylinder 2 having aseries of lenses 3 mounted thereon and rotatedby an electric motor 4,the construction of the, cylinder being shown more clearly in thereceiver shown by Fig. 3. .The lenses 3 are identical in constructionand are mounted in the wall of the hollow cylinder in a spiral. Withinthe cylinder and behind the lenses at the focal point thereof is shown-agroup of four small mirrors 5 which are arranged each to reflect a lightbeam from a different unit area of the picture into the window of one ofthe four photo-electric cells 7. I

The arrangement is such that as each lens 3 passes thegroup of mirrorseach photo-electric cell receives light from a narrow vertical band orstrip of unit areas of the view. Thus, with the apparatus shown, eachlens as it passes the mirrors sends four beams of light to thephoto-electric cells corresponding to the illumination of unit areas infour parallelyertical strips or hands of the View. In one'revolution ofthe cylinder the entire View will have been covered. In accordance withpresent practice in exhibiting moving pictures the cylinder may'beoperated at a speed of approximately sixteen revolutions per second'.If, howcver,a .still picture is to be transmitted and is to be receivedon a light sensitive film or paper instead of being thrown on the screen12 to be observed, a slower speed may suffice. I have shown my inventionapplied to wireless transmission wherein each photo-electric cell 7 isconnected to a device 8 which may include means for amplifying theimpulses received thereby and for producing and modulating a radio carrier wave which may be broadcast from antennae 9. The wave lengths ofthe carrier waves produced by each device 8' will be separated by asuitable interval to facilitate tuning of the receivers used therewith.It is to be understood, however,'that my invention is not ber or screen12, a hollow cylinder 13having a series of lenses 14 set therein in aspiral similar to the cylinder 2 of the transmitter shown in Fig. 1 anda driving motor 15. By suitable means, examples of which are well knownin the art, motors 4 and 15 are caused to run in synchronism, hence thecylinders 2 and 13 rotate synchronously. Within the cylinder 13 and atthe focal point of the lenses 14 are four small mirrors 16 similar tomirrors 5 of Fig. 1. At a point opposite the end of the cylinder13 arefour oscillographs 18 having small mirrors 19 and in a suitable positionto throw light on these mirrors I provide suitable means, shown in thedrawing as comprising four light sources 20. A light beam from each ofthese sources is condensed by a suitable lens 21 on one of theoscillograph mirrors from whence it is reflected to an-. other lens 22and condensed on one of the four mirrors 16. The four light beams reofeach of the four spots of light thrown on the screen is controlledrespectively by the tour oscillographs. For energizing theseoscillographs I have shown four carrier wave receiving sets 25 eachhaving .a receiving loop 26 and tuned to receivethe carrier wavessentout by the respective sending devices 8.

The arrangement is such that as the first lens 14 of the spiral passesthe group of mirrors 16 four spots of light are directed on the screenwhich as the cylinder rotates trace four vertical bands of light acrossone end of the screen. The next lens being slightly offset in an axialdirection causes another four spots to trace another four verticalbandsnext adjacent the first four and so on for each lens of the series,the light spots from the last lens tracing bands across the opposite endof the screen. The cylinder 13 rotates in synchronism with the cylinder3 at the sending station and as each oscillogr aph varies the amountof'light directed on one of the four mirrors 16 in response to the lightreceived by the correspondingly arranged photo-electric cell 7 at thesending station an image of the scene 1 is projected on screen 12. Byemploying a plurality of small mirrors 16 together with a correspondingnumber of lightcontrollingmeans whereby a plurality of light spotssimultaneously sweep across the screen a much more eflicientillumination of the screen is obtained. This plurality feature enablesme 'to employ a fewer, number of rotating lenses and lenses of acorrespondingly larger diameter than would be the case were a singlemirror used and a single spot proj ected by each lens. As a result,the'illumination of the screen increases not merely in direct proportionto the number of small mirrors 16 but at a more rapid rate beingapproximately in proportion to the square of the number of mirrors.

In the modified form of receiver shown in Fig. 4 the light spots arereflected on the screen from a series of rotating mirrors inv stead ofbeing projected thereon by lenses.

The disk 30 connected to be driven by the motor 31 in synchronism withthe cylinder .at the sending station has mounted on its .pe-

riphery a series of mirrors 32. Starting for example with mirror 33 atone end of the series each succeeding mirror is inclined slightly morethan the preceding mirror until the lastmirro'r 34 of the series isreached. Between the mirror disk 30 and the screen 12 is the lens 35 andbetween the lens andthe screen are the four small mirrors 36 correlensesfor similar reasons.

.in the preceding modifications.

meet or, if :desired, may

sponding to the four mirrors 16 of Figs. 2 and 3. As in those figuresalso four oscillographs 18 having mirrors 19 control the amount of lightreceived from the four sources 20 through condensing lenses 21 and 22. Ihave shown the mirror disk 30 rotatable on a vertical axis andthe foursmall mirrors arranged vertically, hence the four light spots traversethe screen horizontally instead of vertically as in the preceding form,the four beams be ing simultaneously reflected by each successive mirroras it comes into position.

In the modified form shown in Fig. 5, I have shown a motor-driven mirrordisk like that in Fig. 4 but in this case the four small mirrors 36 arelocated at one-side of the line lens 38 and are simultaneously reflectedbyeach successive mirror 32 as it'comes into position. As before,controlled respectively by the four oscillographs 18. The same advantagein illumination efliciency may also be obtained w1th the rotatingmirrors as 'with the rotating In the sending apparatus a rotating diskhaving reflecting mirrors such as shown in Fig. 4 or in Fig. 5, may

be usedifdesired instead of the rotating cyl" inder of lenses shown inFig. 1.

' In the modification illustrated in Fig, 6, I have showndiagrammatically a receivlng arrangement whereby the light beams arecontrolled b a bein cause to traverse the image receiving mem er b amirror arrangement like that shown in ig'. 5. Light from a singlesource, \such for example as an arelight 40, after passing through thecondensing lens 41, passes on through the first Nicol prism 42, the cell43, the second Nicol prism 44turned at right angles'to the 45. From thelens 45 the rays converge and are reflected by i the disk 30 to theimage receiving member or screen 12. I have shown the cell 43 diagran1-matically as comprising containing asuitable liquid such as nitrobenzolin which are immersed seven pairs of spaced electrodes 48. 'The platesforming the electrodes are arranged so that light rays may pass throughthe space separating the plates of each pair and thus be subject to theelectrostatic stress therein. The pairs of electrodes are so arrangedrelative to each other that the seven.beams when directed.

upon the screen 12- form seven spots of light and, as the disk 30rotates, trace seven bands of light acrossthe screen instead of four asThe several bands may just slightly overlap. One electrode of each pair48 has a separate connection 49 extending the four light beams are formof Kerr cell, the beams the respective mirrors 32 of the glass vessel 47s without the cell while the remaining electrodes are connected togetherforconvenience by a single connection 50. The seven pairs of electrodesare thus adapted to be independently controlled for example from acorresponding number of receivers 25 or from a radio carrier current ofseven channels of the Hammond type. The two prisms 42 and a l arearranged to produce planes of polarization at right angles to each otherso that when there is no field between the electrodes the light beamsare shut OK but when a field is applied to any of the pairs ofelectrodes the plane of polarization is thereby twisted so that light islet through at that point. Seven independentlf varying beams of lightthus simultaneously traverse the screen with the passage of each mirror.

The advantages of the multiple beam system illustrated by rotatablelenses and rotating mirrors applies equally toother well known methodsof analyzing the picture such as vibrating mirrors. A reduction of therate of vibration to one-fourth, as shown, makes it possible to-use alarge mirror and thus gain in total illumination by increase of thebrilliancy of each light spot in addition tothe direct gain by usingfour beams instead of one. It is to be understood that the terms light?and illumination as used in the description and claims are notrestricted to those rays which constitute the visible portion of thespectrum but apply equally Well to the invisible portions of thespectrum for under certain conditions it may be more desirable to makeextensive use of the invisible rays in the transmitting apparatus andthis also may be done in the receiving apparatus, particularly 1f it isconstructed to reproduce the picture photographically insteadofvisually. 1

What I claim. as new and desire to secure by Letters Patent of theUnited States, is:

l. The method of transmitting pictures which comprises simultaneouslyscanning a' group of adjacent bands of unit areas, successively Scanningadjacent groups of saidbands,

and producing electric currents correspond ing with the tones of thepicture indicated by the light emitted by said unit areas.

2. The method of transmitting pictures which comprises simultaneouslyscanning a group of bands of adjacent unit areas, successively scanningdifferent groups of said bands, and producing electrical variationscorresponding with the variations of the picture as indicated by thelight emitted from said unit areas.

3. In picture transmission, the method of receiving a transmittedpicture on an image receiving member which comprises scanning the membersimultaneously. with a group of adjacent light beams, independentlyvarying the intensity of the beams, and successively scanning adjacentareas of said member with said group of light beams.

5. The method of transmitting-a picture to an image receivingmember at adistant point,

which comprises simultaneously scanning a group of adjacent bands ofunit areas, successively scanning different groups of saidv bands,producing electrical variations corresponding to variations in the colorof said unit areas, scanning the receiving member by a plurality oflight beams, and varying the several light beams in accordance 'With therespective electrical variations.

6. Apparatus for the transmission of pictures comprising means forsuccessively scanning adjacent groups of bands of unit areas of thepicture to be transmitted, and means for producing electrical variationscorresponding to the variations of the picture as successivelydetermined simultaneously by the unit areas of said groups.

7-. Apparatus for the transmission'of pictures comprising meansforsuccessively scanning adjacent groups of bands of unit areasof thepicture to be transmitted, and a plurality of photo-electric devicesarranged to receive light simultaneously'from the different single unitareas of one of said groups.

8. Apparatus forthe transmission of pictures comprising means forsuccessively scanning adjacent groups of bands of unit areas of thepicture to be transmitted, a plural ty of photo-electric devicesarranged to receive light respectively from said unit areas andelectrical transmitting means respectively responsive to said devices.

9. Apparatus for the transmission of pictures comprising an imagereceiving member, means for simultaneously moving a group of adjacentlight beams over a part of said member, means for causing said group oflight beams to'be moved successively over difierent parts of saidmember, and means for controlling the intensity of the respective lightbeams. I 10. Apparatus for the transmission of pictures comprising animage receiving member,

a plurality of electrical receiving means,

means for projecting a plurality of adjacent beams of light onsaid-member, means for controlling the intensity of said beamsrespectively by said receiving means,'and means for causing said beamssimultaneously to sweep across a part of sand image receiving member andfor causing sard beams to be successively swept across different partsof said member.

11. Apparatus for the transmisslon of pletures comprising an imagereceiving member, a receiver comprising a plurality of means forindependently receiving electrical I variations, means for 5 of adjacentlight beams,vmeans for c0ntrolling the intensity of said beamsrespectively n by said receiving means, and a rotatable memproducing aplurality her having a plurality of light directing units, eachsuccessive unit being arranged to project simultaneously said lightbeams on a diflerent part of said member.

In Witness whereof, I have hereunto set my hand this 18th day of October1926.

ERNST F. W. ALEXANDERSON.

